7th Grade · Geometry
Circumference
7.G.B.4
Definition
The distance around a circle. C = πd = 2πr. Measured in linear units (cm, m, in).
Examples
- Using radius: C = 2π(7) ≈ 43.96 cm.
- Using diameter: d = 10 m, C = 3.14 × 10 = 31.4 m.
Key rule
Use C = πd when you know the diameter; use C = 2πr when you know the radius.
Memory hook
Circumference is the circle's perimeter, straightened out.